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Variable K + channel subunit dysfunction in inherited mutations of KCNA1
Author(s) -
Rea Ruth,
Spauschus Alexander,
Eunson Louise H.,
Hanna Michael G.,
Kullmann Dimitri M.
Publication year - 2002
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2001.013242
Subject(s) - mutant , wild type , protein subunit , mutation , biology , green fluorescent protein , phenotype , microbiology and biotechnology , genetics , gene
Mutations of KCNA1 , which codes for the K + channel subunit hKv1.1, are associated with the human autosomal dominant disease episodic ataxia type 1 (EA1). Five recently described mutations are associated with a broad range of phenotypes: neuromyotonia alone or with seizures, EA1 with seizures, or very drug‐resistant EA1. Here we investigated the consequences of each mutation for channel assembly, trafficking, gating and permeation. We related data obtained from co‐expression of mutant and wild‐type hKv1.1 to the results of expressing mutant‐wild‐type fusion proteins, and combined electrophysiological recordings in Xenopus oocytes with a pharmacological discrimination of the contribution of mutant and wild‐type subunits to channels expressed at the membrane. We also applied confocal laser scanning microscopy to measure the level of expression of either wild‐type or mutant subunits tagged with green fluorescent protein (GFP). R417stop truncates most of the C‐terminus and is associated with severe drug‐resistant EA1. Electrophysiological and pharmacological measurements indicated that the mutation impairs both tetramerisation of R417stop with wild‐type subunits, and membrane targeting of heterotetramers. This conclusion was supported by confocal laser scanning imaging of enhanced GFP (EGFP)‐tagged hKv1.1 subunits. Co‐expression of R417stop with wild‐type hKv1.2 subunits yielded similar results to co‐expression with wild‐type hKv1.1. Mutations associated with typical EA1 (V404I) or with neuromyotonia alone (P244H) significantly affected neither tetramerisation nor trafficking, and only altered channel kinetics. Two other mutations associated with a severe phenotype (T226R, A242P) yielded an intermediate result. The phenotypic variability of KCNA1 mutations is reflected in a wide range of disorders of channel assembly, trafficking and kinetics.